Add retry support to quic_client_interop_test

gfe-relnote: n/a, test-only
PiperOrigin-RevId: 274644470
Change-Id: Ie68fd26ad452d6489d3fffeba88bcb2bf54e475d
diff --git a/quic/core/quic_connection_stats.h b/quic/core/quic_connection_stats.h
index 17a3a1e..805afd1 100644
--- a/quic/core/quic_connection_stats.h
+++ b/quic/core/quic_connection_stats.h
@@ -106,6 +106,9 @@
 
   // Number of connectivity probing packets received by this connection.
   uint64_t num_connectivity_probing_received;
+
+  // Whether a RETRY packet was successfully processed.
+  bool retry_packet_processed;
 };
 
 }  // namespace quic